1. Technical Field Text
Embodiments are directed to the general field of mobile cranes and more particularly to telescoping members such as booms.
2. Background Information
FIG. 1 illustrates a crane 10 having a chassis 11 and upper works 13. Because the crane 10 is mobile and may be moved while on site, and is also transported from site to site, the crane 10 is sized to travel over the road and for transport on commonly available transport systems. Due to size constraints, the crane 10 includes extendable components to allow the crane 10 to increase in dimension while at the job site. For example, in FIG. 1, the crane 10 has a telescoping boom 12. The minimum length of the boom 12 must be short enough for safe highway travel, as well as travel around a job site. However, a lift job typically requires a much longer boom 12. To allow for a longer boom 12, the crane 10 has multiple boom segments that the nest within one another.
While the general concept of a telescoping boom 12 is fairly straightforward, its actual implementation is complex. In order to achieve a maximum length, a telescoping boom 12 typically has multiple sections, with each section nesting in an adjacent section. FIG. 2 illustrates an enlarged view of the tip of the boom 12 of the crane 10 of FIG. 1. This boom 12 has a base section 16, three intermediate sections 18, 20, 22, and an inner section 24. These sections each extend and retract depending on the necessary length of the boom 12. Furthermore, a single drive system, such as an inverted hydraulic actuator, is used to move the sections 18, 20, 22, 24 in and out of the base section 16. The use of a single drive avoids the excess weight that would result from the use of multiple drive systems. Once a section is extended from the base section 16, it is locked to the section it is nested within.
FIG. 3 illustrates a schematic of a drive system for extending a boom in the form of an inverted hydraulic actuator 26. The inverted hydraulic actuator 26 is located within the base section 16 with a rod 28 connected to the base section 16 and a cylinder 30 that is free to move relative to the base section 16 when the inverted hydraulic actuator 26 is actuated. A pinning head 32 is disposed at a rod end of the cylinder 30 and has a cylinder-to-boom section pin 34 for pinning the pinning head 32 to a boom section and a boom section connection pin actuator 36 for actuating a pin to lock adjacent boom sections together once extended.
In operation, the pinning head 32 actuates the boom section pin 34 to pin the inner boom section 24 to the cylinder 30. The cylinder 30 is actuated, moving the inner section 24 out of the base section 16. Once the inner section 24 is extended to a desired distance, the inner section 24 is pinned to the next boom section 22 with the boom section connection pin actuator 36. The cylinder to boom section pin 34 is then released from the inner boom section 24 and the cylinder 30 is retracted. Once retracted, the pinning head 32 is pinned to the next section 22 with the cylinder-to-boom section actuator 34. The next section 22 extends from the base section 16, pushing the inner section 24, which is now pinned to the next section 22, out farther as well. Once extended, section 22 is pinned to section 20 with the boom section connection pin actuator 36 to lock the sections together. The cylinder-to-boom section pin actuator 34 is released and the cylinder 30 is retracted. This process continues, extending boom sections until the desired boom length is achieved.
The pinning head 32 is responsible for at least two pinning operations. The first is actuating the boom section connection pin 36 to couple the boom sections together. This is done with a small hydraulic actuator 37 mounted parallel to the inverted hydraulic actuator 26 as shown in FIG. 3. The second pinning operation actuates a pin laterally, perpendicular to the direction of travel of the boom sections; this pinning operation is performed with hydraulic pressure exposed to surfaces of the pin internal to the pinning head 32. However, this pin translation is perpendicular to the main actuator.
To simplify the design, each of the hydraulic actuators operates using the same hydraulic source as the main inverted hydraulic actuator 26. The pressurized hydraulic fluid is controlled by a control valve 38 which selectively pressurizes the boom section connection pin actuator 36 or the cylinder to boom section pin actuator 34. Because the control valve 38 and the and pin actuators 34, 36 move with the telescoping cylinder 30, the hydraulic line 40 needs to adjust to compensate for the varying distance between the hydraulic pressure source and the actuators 34, 36. This may be accomplished through a trombone tube which extends in length when the telescoping cylinder 30 is extended. However, because the tube's internal volume changes as the cylinder 30 is retracted and extended, the speed at which the cylinder 30 is retracted and extended is limited to avoid excessive pressure changes in the trombone tube.
Current pinning systems such as that shown in FIG. 3 suffer from further shortcomings such as being a dead end system. It is very difficult to bleed air from the system since there is no return flow from the pinning actuators 34, 36. The control system is also very complicated for a hydraulic system, requiring the cylinder 30 to be actuated across large distances (such as 10 meters) while extending boom sections, and then precisely positioned to within 5 mm of a pinning hole for pinning the cylinder 30 to a section. To improve validation of cylinder 30 positioning, current systems may use proximity switches within the pinning head 32 (which are in a virtually unmaintainable location), and proximity switches with the pinning head components near the boom section weldment. This requires a large amount of control system complexity and precision assembly procedures.
Finally, in addition to complexity to position cylinder 30 to a boom section, there is no use of a positive identification of the boom section being approached or connected to. Thus, the system must keep track of where the cylinder 30 is and which boom sections it has connected in the past. Furthermore, this logic must be kept in non-volatile memory so that after a power cycle, the control system still knows where the sections were from the previous use.
What is needed is a telescoping boom that addresses the shortcomings in current boom design. It would be beneficial if the system was simpler than existing systems while allowing the boom to extend and retract rapidly independent of the lock actuators.